This invention relates to nozzle constructions for fuel injectors.
Increasing concern in recent years over emissions from internal combustion engines has led to substantial re-evaluation of nozzle constructions for fuel injectors. Many fuel injectors have substantial so-called "sac" volumes within their nozzle tips. During the engine cycle, a small amount of fuel remains within the sac volume in the nozzle tip. During the latter stages of the combustion process, such fuel is vaporized but is in a sufficient quantity that it does not participate in the combustion process. As a consequence, it is emitted from the engine as a hydrocarbon emission.
As a consequence of the relatively high emissions of such constructions, so-called zero sac fuel injection nozzles have come into vogue. In such nozzles, a valve member typically is located on the exterior of the nozzle and seals against the injection opening from the exterior thereof after the injection process has been completed. As a result, there is no sac volume exposed to the hot gases of combustion to be vaporized and emitted.
While zero sac nozzles have been successful in eliminating or reducing hydrocarbon emissions, in most instances, their life is not as long as that of nozzles having a sac volume. Specifically, in nozzles having a sac volume, the evaporation of fuel from the sac volume cools the nozzle, thereby preventing oxidation of nozzle parts and minimizing the formation of lacquer on the valve components which would interfere with fuel delivery and sealing qualities.